Transparent conductive substrates having a transparent metal oxide conductive layer (such as ITO and ZnO) formed on a transparent substrate are used for touch panels, solar cells, electromagnetic wave/electrostatic shields, ultraviolet/infrared ray shields, and other applications because of their transparency and conductivity.
However, conventional products have the following drawbacks.    1) The light reflection of visible light on the surface of metal oxide conductive layers is large, and their transparency is poor.    2) Metal oxide conductive layers absorb light at around near ultraviolet ray; therefore, the transmittance of light wavelengths of <450 nm decreases, resulting in yellowing of the layers.Because of the above drawbacks 1) and 2), the difference between portions having a pattern and portions having no pattern can be clearly recognized when metal oxide conductive layers are pattern-etched in use. The improvement thereof is thus also needed.    3) Because of the thinness of ITO films, scratches due to abrasion are generated during transportation, processing, and use of the films, causing the occurrence of defects such as deterioration in conductivity, disconnection, and deterioration in appearance.    4) Since water wettability on ITO films is poor, improvement of printing and coating onto ITO films, as well as of adhesion properties of adhesives or the like, has been an issue to be addressed; and there is a need for improvement in water wettability (decrease in contact angle of water) on the film surface.
To improve these drawbacks, films in which a transparent layer (e.g., SiO2, Al2O3, transparent resins) whose refractive index of light is smaller than that of ITO is formed on the surface of an ITO film have been proposed (for example, Patent Literature 1 and 2).
Patent Literature 1 discloses a method for producing a transparent conductive film, in which after a high-frequency sputter etching treatment is applied to the surface of a polyethylene terephthalate film, a transparent conductive thin film is formed thereon, and a transparent dielectric thin film having a film thickness of 100 Å or more is formed on the transparent conductive thin film. By forming the dielectric thin film, enhancement of scratch resistance and improvement in transparency are attempted.
Patent Literature 2 discloses a transparent conductive laminated body in which a transparent conductive thin film is formed on one surface of a transparent film substrate having a thickness of 2 to 120 μm, a transparent dielectric thin film is formed on the conductive thin film, and a transparent substrate is adhered to the other surface of the film substrate via a transparent adhesive layer. By forming the dielectric thin film, transparency and scratch resistance are enhanced, and improvement in operability as a characteristic of touch panels is also attempted.
By such layer formation, the above-mentioned drawbacks can be improved. However, because such a transparent dielectric thin film is an electrical insulation layer, conductivity between a metal oxide conductive layer and an electrode (such as a conductive paste layer and a metal layer) disposed on the dielectric thin film layer is very poor and unstable. In addition, because of the presence of the electrical insulation layer, it is difficult to pattern-etch the metal oxide conductive layer (ITO) film when needed.
For these reasons, transparent conductive substrates having a dielectric thin film layer formed on a metal oxide conductive layer, which are unsuitable for applications in which ITO film etching and a lead electrode are required, such as touch panels and solar cells, have limited applications.
Patent Literature 3 discloses an inorganic microporous film having ultrafine pores with an average pore diameter of 0.1 nm to 10 μm that penetrate straight through with substantially the same diameter from the front surface to the rear surface of the film, and that this inorganic microporous film is produced by depositing an inorganic material in an oblique manner. Separate films, polarizing films, catalyst carrying films, colored films, and the like are mentioned as applications of the inorganic microporous film.